Sound is measured in decibels. Even after long exposure, sounds of less than 85 decibels are unlikely to cause hearing loss.
As the decibel level goes up, however, the risk of damage increases. At 85 decibels and above, long or repeated exposure can cause hearing loss. The louder the sound, the shorter the time it takes to damage hearing.
5 Things You Can Do To Protect Your Child's Hearing
Limit the amount of time your child listens to headphones. This is hard, but worth it. While hearing can be damaged from a single, loud sound, like a bomb going off, hearing loss happens most often when kids listen to loud music for extended periods of time. By all means do not let your kids sleep with earbuds in their ears.
Take your child to a park and teach him to appreciate the sounds of nature. Bird song, wind in the trees, even silence is beautiful. In our noisy world we don’t hear these sounds enough.